The use of low-cost transducers such as piezoelectric diaphragms in structural health monitoring (SHM) applications based on the electromechanical impedance (EMI) method has grown in recent years. Although many studies report the feasibility of such transducers for impedance-based damage detection, the experiments are typically performed on small structures. Therefore, the objective of this work is to perform an experimental analysis of the feasibility of the piezoelectric diaphragms for the detection of damage in large structures. Several tests were carried out on a large aluminum plate in which a diaphragm was attached. The electrical impedance signatures of the transducer were collected and a basic damage index was calculated in order to verify the feasibility of quantifying the size of the damage at different distances from the transducer. The experimental results indicate that the piezoelectric diaphragms have a good sensitivity to provide a damage size classification in large structures. In addition, the sensitivity to damage detection and classification decrease as the distance between the transducer and the damage increases. Therefore, the results reported in this study indicate that low-cost piezoelectric diaphragms are feasible for impedance-based SHM applications in large structures.

Piezoelectric transducers have been extensively used in various applications in recent decades, such as in the non-destructive testing (NDT) of materials and structures. A piezoelectric transducer commonly used in NDT applications is lead zirconate titanate (PZT) ceramic, which is thin, lightweight, and minimally invasive to the structure. In this study, we analyzed the use of commercial piezoelectric diaphragms for damage detection based on the electromechanical impedance (EMI) method, which is an NDT technique used in structural health monitoring (SHM) applications. The commercial diaphragms have the advantages of being low cost and readily available. To assess their feasibility for damage detection, a low-cost diaphragm was compared with a conventional PZT ceramic with similar shape and dimensions. Tests were performed on aluminum beams, in which damage was simulated by placing a metallic bolt at different distances from the transducers. The sensitivity to damage was estimated using the correlation coefficient deviation (CCD) damage index, which was calculated using the electrical impedance signatures obtained from each transducer. The experimental results indicate that the piezoelectric diaphragms are able to detect damage; therefore, this study provides an important contribution to the field of SHM systems based on the EMI method.

Abstract: Mitigation of global carbon emissions to prevent global warming potential using biofuels is highly dependent on direct and indirect land use change (LUC). There are still several uncertainties about how to assess the indirect LUC impacts of biofuels. However, direct LUC (dLUC) can be evaluated using remote sensing (RS). The present work has the aim to quantify the dLUC occurred during the recent sugarcane expansion for ethanol and sugar production concentrated in the South-Central region of Brazil. This region has a favorable climate for sugarcane production and also a great potential for agriculture expansion. Yearly monitoring from 2005 to 2010 using Landsat type imagery has shown that the sugarcane crop expanded during this period over 3.5 Mha in the South-Central region. To evaluate the dLUC in response to the expanded sugarcane area we used RS time series from the MODIS sensor transformed to the two-band enhanced vegetation index (EVI2), acquired from 2000 to 2009. The original sugarcane map was re-sampled to a pixel size of 250 x 250 m to be compatible with spatial resolution of the MODIS images. One percent of these pixels were systematically sampled covering 1035 pixels. Each of these pixels were carefully analyzed using a special developed web tool to visualize the entire MODIS time series overlaid with several Landsat-5 TM images acquired at key periods in order to correctly identify the land use/land cover prior to the sugarcane crop. Considering 2000 as reference year for the dLUC evaluation it was observed that: 69.8% of the sugarcane expanded on pasture land; 26.2% expanded on annual crops; 0.6% expanded on native vegetation; and 3.4 % was not sugarcane expansion but sugarcane renovation using crop rotation. It was interesting to notice that 35% of the pasture land in 2000 converted to sugarcane was first converted to annual crops. This practice is commonly adopted for one to two years on degraded pasture to improve the physical soil characteristics before introducing the sugarcane crop. It was also observed that the 0.6 % of native vegetation changed to sugarcane was previously converted to either annual crop (33%) or pasture land (67%). Although the analysis needs to be further refined the results clearly show that the dLUC observed during the recent sugarcane expansion for ethanol and sugar production in the South-Central region of Brazil is mainly occurring on pasture and agricultural land.